As a communication system succeeding W-CDMA and HSDPA, an LTE (Long Term Evolution) system is being worked on by the 3GPP (3rd Generation Partnership Project), which is the standardization group for W-CDMA. In the LTE system, an OFDMA (Orthogonal Frequency Division Multiple Access) system is being considered for the downlink, and an SC-FDMA (Single-Carrier Frequency Division Multiple Access) system is being considered for the uplink.
In the OFDMA system, a frequency bandwidth is divided into plural narrower frequency bandwidths (subcarriers), and data are transmitted by being carried on one of the narrower frequency bandwidths. By contiguously arranging the subcarriers without interfering with each other though the subcarriers may be partially overlapped, it becomes possible to achieve fast transmission and improve the use efficiency of the frequency bandwidths.
The SC-FDMA is a transmission system in which a frequency bandwidth is divided so that plural terminals can transmit using different frequency bandwidths among the terminals to reduce the interference between the terminals. The SC-FDMA has the characteristic of small variation of the transmitting power. Therefore, the configuration of the transmitter of the terminal can be relatively simplified.
In addition, as transmission methods in a downlink data channel, there are localized transmission and distributed transmission.
In localized transmission, as shown in FIG. 1A, frequency resources are allocated to each user by frequency blocks. For example, in localized transmission, the frequency blocks having good frequency selective fading are allocated. Generally, localized transmission may be effectively used when the size of the transmission data is large and the frequency scheduling effect is required to be enhanced.
In distributed transmission, as shown in FIG. 1B, data are spread (distributed) across the entire available bandwidth without relation to the frequency blocks and transmitted. For example, distributed transmission is generally used when the frequency scheduling may not be performed due to fast movement of users and when the size of the transmission data is small such as the case of VoIP.
In LTE system, it is required for a single system to support various sizes of packets ranging from packets having a larger size used in browsing a Web site or the like to packets having a smaller size used in VoIP or the like in communications with slow moving users and fast moving users as well.
To support both localized transmission and distributed transmission by a single system, there has been proposed a communication device in which, when distributed transmission is performed at the resource block level, one resource block is divided into plural divided blocks, and the divided blocks are allocated as the resource blocks.
This communication device generates control information with respect to a mobile station to which the resource blocks are allocated. For example, identification codes, such as identification numbers indicating the physical locations of the plural resource blocks that have been formed by dividing a system bandwidth (namely, an allocated bandwidth) are allocated.
In this case, a division number of the resource blocks to be used for distributed transmission among the plural resource blocks is set equal to an allocation unit of the divided resource blocks to be allocated to a mobile station as a unit and is defined as “ND” (where ND is an integer number greater than 0). FIG. 2A shows a case where ND=2. According to FIG. 2A, in a case of ND=2, each of the resource blocks used for distributed transmission is divided into two parts (divided resource blocks), and the two divided resource blocks, namely a pair of the divided resource blocks becomes a unit to be allocated to a mobile station. In this case, the physical locations of the resource blocks used for distributed transmission are determined in advance in accordance with the total number of resource blocks used for distributed transmission.
As shown in FIG. 2B, a specific signaling format for transmitting the allocation information includes each field for an ID (UE-ID) of an allocated mobile station, a transmission type indicating which of localized transmission or distributed transmission is to be performed, and allocation information with respect to each resource block, namely, the resource block for localized transmission and the resource block for distributed transmission. In the fields for the allocation information with respect to the resource blocks, subfields corresponding to the resource blocks are provided, and information of allocated or non-allocated is assigned to the subfields. An assigning method of the allocation information with respect to each of the resource blocks is called “bitmap”. A base station transmits control bits including such allocation information of as many numbers as the number of mobile stations allocated to perform localized transmission and distributed transmission.
Non Patent Document 1: 3GPP, R1-061896, Motorola, June 2006
Non Patent Document 2: 3GPP, R1-061308, NEC “Resource Allocation Signaling for E-UTRA,” May 2006